Is peptide transport important for the legume:rhizobia symbiosis?
- La Trobe University, Bundoora, Victoria.
- University of Sydney, Sydney, NSW.
- Flinders University of South Australia, Adelaide, SA.
- University of Bern, Bern, Switzerland.
The symbiosome membrane is a plant-derived membrane that surrounds rhizobia in nitrogen-fixing nodules, separating them from the plant cytoplasm. The membrane controls the transport of compounds into and out of the symbiosome and is likely to be a key point of regulation for the interaction between legumes and rhizobia in the symbiosis. We recently completed a proteomic analysis of the soybean symbiosome membrane (Clark et al. 2015 MCP 14:1301-22.). Among the proteins we identified were many putative transport proteins including members of families encoding transporters for sulphate, calcium, and hydrogen ions, as well as aquaporins. A number of proteins were part of the nitrate transporter 1/ peptide transporter family (NPF), which includes a range of transporters for nitrogen containing compounds including nitrate, peptides, glucosinolates, and plant hormones. We have used yeast complementation to show dipeptide transport by one of the NPF members that is expressed specifically in infected cells of mature nodules. Another transporter identified on the symbiosome membrane has been characterised as an oligopeptide transporter from the Yellow-stripe-like family. When we silenced the genes encoding these peptide transporters nitrogen fixation was inhibited suggesting an important role for peptide transport in determinant nodules.